The present application claims priority to Japanese Application No. P2000-072513 filed Mar. 10, 2000, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to a thin type solid electrolyte battery and a production method thereof.
In recent years, along with the progress of the electronic technology, there have been strong demands toward higher performances, miniaturization, and portableness of electronic apparatuses. To meet such demands, batteries used for these electronic apparatuses have been required to have high energy densities, and from this viewpoint, studies have been actively made to develop nonaqueous electrolyte batteries. In particular, lithium batteries or lithium ion secondary batteries, having excellent performances, for example, electromotive forces higher than those of conventional batteries, such as 3 or 4 V, have been adopted for various portable electronic apparatuses such as cam coders, portable telephones, and notebook type personal computers.
Of the above-described lithium ion secondary batteries, a solid electrolyte battery using a solid electrolyte, having merits, for example, a property allowed to be thinned and freely foldable, has been actively studied. Examples of the solid electrolytes may include a gel-like electrolyte composed of a solid electrolyte containing a plasticizer and a high polymer solid electrolyte composed of a high polymer in which a lithium salt is dissolved.
To make effective use of the merits, that is, the characteristics allowed to be thinned and reduced in weight, of these nonaqueous electrolyte batteries, for example, Japanese Patent Laid-open No. Sho 57-115820 has disclosed a nonaqueous electrolyte battery of a type in which a battery element is enclosed by using, as a container, a so-called laminate film formed by holding metal foil or a metal layer such as a metal vapor-deposition layer between resin layers. In this battery, a heat seal layer constituting the innermost layer of the container, that is, the laminate film is made from a resin such as acrylic acid denatured polyethylene or acrylic acid denatured polypropylene ionomer, which resin exhibits a relatively good air-tightness at ordinary temperature. However, batteries mounted on recent electronic apparatuses, for example, personal computers have been required to exhibit a heat resistance at 85xc2x0 C. In such a high temperature environment, the above-described nonaqueous electrolyte battery may cause a problem that the resin forming the heat seal layer be peeled from the metal layer, thereby degrading the air-tightness of the battery.
To solve the above problem, Japanese Patent Laid-open No. Hei 9-288996 has disclosed a nonaqueous electrolyte battery of a type in which an insulating layer made from a material excellent in a barrier performance against an electrolytic solution such as polyethylene terephthalate is disposed between a heat seal layer constituting the innermost layer and a metal layer of a container. In this battery, by heat-sealing the container in which the insulating layer is provided between the heat seal layer and the metal layer, it is possible to prevent the peeling of the heat seal layer from the metal layer by suppressing permeation of the electrolytic solution between the metal layer and the heat seal layer, and hence to ensure a relatively high air-tightness even in a high temperature environment.
However, in the case of using the container having the above-described heat seal layer for a thin type sheet-like solid electrolyte battery, the container becomes thick because of the presence of the heat seal layer, to thereby increase the total thickness of the solid electrolyte battery. That is to say, because of the container including the heat seal layer, it fails to make effective use of the merits of the solid electrolyte battery, that is, the characteristics allowed to be thinned and reduced in weight. Further, since the proportion of the constituent elements not contributing to the battery reaction to the entire battery becomes large, there occurs an inconvenience that the energy density per weight and the energy density per volume are reduced.
The solid electrolyte battery using the container including the heat seal layer presents another problem that since the resin forming the heat seal layer is exposed from a side surface of the outer peripheral edge portion of the container, the inner side of the heat seal layer is exposed to the electrolytic solution and the outer side thereof is exposed to outside air, with a result that a trace of moisture permeates the interior of the battery through the exposed heat seal layer with elapsed time, thereby deteriorating the cycle characteristic of the battery.
A further problem of the solid electrolyte battery using the container including the heat seal layer is that the width of a so-called sticking margin given to the outer peripheral edge portion of the container must be extended for desirably heat-sealing the container. As a result, since the area of the sticking margin not contributing to the battery reaction becomes large, the energy density of the battery is degraded.
An object of the present invention is to provide a solid electrolyte battery allowed to be further thinned and reduced in weight, to be improved in energy density per weight and energy density per volume, and to be enhanced in air-tightness, and to provide a method of producing the solid electrolyte battery.
To achieve the above object, according to a first aspect of the present invention, there is provided a solid electrolyte battery including: a first electrode including a first collector, and a first active material layer formed on one surface of the first collector with an outer peripheral edge portion of the first collector remaining as a collector exposed portion; a second electrode including a second collector and second active material layers formed on both surfaces of the second collector; and a solid electrolyte interposed between the first electrode and the second electrode; wherein the second electrode is held in the first electrode in such a manner that the first active material layer is opposed to each of the second active material layers via the solid electrolyte, and is sealed in the first electrode by joining the collector exposed portion of the first electrode to each other.
With this configuration, since the first collector serves as the container, it is possible to eliminate the need of provision of a terminal through which the first electrode is connected to the external and also provision of the container. Further, since the collector exposed portion of the first electrode is directly joined to each other not via a resin for heat seal, it is possible to obtain a significantly desirable air-tightness and also to significantly reduce the area of the collector exposed portion of the first electrode functioning as the joining margin.
To achieve the above object, according to a second aspect of the present invention, there is provided a method of producing a solid electrolyte battery, including the steps of: forming a first active material layer on one surface of a first collector with an outer peripheral edge portion of the first collector remaining as a collector exposed portion, to produce a first electrode; forming second active material layers on both surfaces of a second collector, to produce a second electrode; holding the second electrode in the first electrode in such a manner that the first active material layer is opposed to each of the second active material layers via a solid electrolyte; and joining the collector exposed portion of the first electrode, in which the second electrode has been held in the holding step, to each other, to seal the second electrode in the first electrode.
With this configuration, since the collector exposed portion of the first electrode functioning as the joining margin is directly joined to each other not via a resin for heat seal to be thus sealed, it is possible to produce a thin, lightweight, and air-tight solid electrolyte battery.